Embodiments of the invention relate to a reference current circuit for providing a temperature compensated reference current.
Conventional bandgap circuits generate a reference current or a reference voltage by combining two voltage drops, the first voltage drop having a positive temperature coefficient and the second voltage drop having a negative temperature coefficient, so that the resulting reference current or reference voltage is substantially temperature independent. Such bandgap circuits may comprise bipolar transistors and the voltage drops are the base-emitter voltage drops (VBE). Such bandgap circuits may be used for providing to electronic devices a desired reference current or a desired reference voltage. The bandgap circuit may be provided as a separate circuit element or may be formed together with the electronic device. For example, the bandgap circuit may be formed using the SiGe:C (silicon germanium) technology. Implementing the bandgap circuit in this technology uses silicon germanium (SiGe) transistors having a characteristic base-emitter voltage drop (VBE) of about 0.8 V. Such bandgap circuits will not operate below 2V.
However, new trends in electronics and semiconductor technology may require further reduction in power consumption so that devices may be required to operate at voltages in the range below 2V, e.g., between 1V and 1.5V. The above described conventional bandgap circuits are designed to provide supply voltages down to 2V but not down to 1V to 1.5V so that a redesign of such conventional bandgap circuits would be required. For example, since bandgap circuits comprise series-connected BE-junctions, a semiconductor technology using silicon germanium transistors offers base-emitter voltage drops of around 0.8V. With two silicon germanium transistors connected in series a voltage drop of 1.6 V is applied to the circuit which requires supply voltages above at least 1.6V, in general above 2V. Thus, any redesign of such a conventional bandgap circuit would require a new design approach that uses different materials having, e.g., smaller bandgap voltages as silicon germanium. However, changing the technology is expensive and semiconductor materials with a smaller voltage drop may be very expensive in the manufacturing process.